The world war began in Europe and spread around the globe. Its causes are the subject of many debates.
One theory is that the war was caused by a delicate balance of structural forces that led to an interruption in the normal incentives for peace. This caused opponents to take a stand that they had never taken before, and thus break the natural compulsion for compromise.
This happened when the assassination of Archduke Franz Ferdinand in Sarajevo triggered a crisis among Europe’s major powers. A political balance was disrupted that set off a wave of violence that spread from one corner of the globe to the other.
In the west, the German army followed the well-designed Schlieffen Plan and invaded Belgium and France. Britain joined the French and pushed the Germans back from around Paris, creating the Triple Entente.
By August, battles had erupted along the Western Front and the armies were stuck in a vast quagmire of trenches. They were defended by barbed wire, explosive mines, and artillery fire. The defenders, dug into the ground, were much safer against enemy artillery and could resist advancing attackers more easily.
As the war progressed, new countries entered the conflict in an attempt to reclaim land that they had lost previously to Russia and Austria-Hungary. These countries included the Ottoman Empire and Italy. The war would eventually result in the annihilation of these powerful empires.